Method of producing CRT funnel glass suitable for glass recycling, and CRT funnel glass

ABSTRACT

On producing CRT funnel glass, Fe 2 O 3  is added in a range of 0.05 to 1 mass % into a glass material of the CRT funnel glass so that a fluctuation of transmittance of light having a wavelength of 1,050 nm becomes 10% or less in a thickness of 10 mm of the CRT funnel glass. As a glass material of the CRT funnel glass, CRT panel glass or CRT frit may be used.

BACKGROUND OR THE INVENTION

[0001] The present invention relates to a method of producing funnel glass for a CRT (cathode ray tube), and further relates to such CRT funnel glass.

[0002] An envelope of a CRT comprises a panel portion for projecting video images, a tubular neck portion with an electron gun arranged therein, and a flare-shaped funnel portion connecting the panel portion and the neck portion with each other. The panel portion, the neck portion and the funnel portion are in the form of glass members, respectively. Electron beams emitted from the electron gun excite phosphors arranged on an inner surface of the panel portion to emit light so that the video images are projected on the panel portion. At this time, X-rays bremsstrahlung are produced inside the CRT. X-rays bremsstrahlung adversely affect human bodies when leaked to the exterior of the CRT through the envelope. Therefore, the envelope of this type is required to have a high X-ray absorbability.

[0003] CRTs are classified broadly into a black-and-white CRT bulb and a color CRT bulb. Generally, a panel portion of the black-and-white CRT bulb (hereinafter referred to as “black-and-white panel”) is required that its glass is not colored due to electron beams and X-rays. The black-and-white panel is made of glass containing about 5 mass % of PbO. A panel portion of the color CRT bulb (hereinafter referred to as “color panel”) is used at higher voltages as compared with the black-and-white panel, and thus is required more severely that its glass is not colored due to electron beams and X-rays. Therefore, the color panel is made of glass containing no PbO but containing SrO and BaO. The funnel portion is required to have a high X-ray absorption coefficient, and thus is made of glass containing no less than 10 mass % of PbO. The panel portion and the funnel portion are joined together by welding in case of the black-and-white CRT bulb, and by using a PbO frit made of glass containing PbO as a bonding agent in case of the color CRT bulb.

[0004] On the other hand, in recent years, recycling of CRT bulb glass members has been advanced. Specifically, glass members of CRT bulbs are first classified into black-and-white bulb glass members and color bulb glass members, which are then further classified into groups of panel glass members, funnel glass members and neck glass members. Then, the glass members are immersed per group into a chemical liquid to remove phosphors, carbon DAGs, frits and so on. Subsequently, the glass members are comminuted per group and the comminuted glass members are used as a glass material for producing glass members of the same group, so that recycling is carried out.

[0005] The reason why the glass members should be strictly classified as described above is that, for example, if the glass members containing PbO, such as the black-and-white panels, are mixed into a glass material of the color panels, the color panels made of this glass material are subjected to coloration due to electron beams and X-rays.

[0006] Further, if the frits are not removed completely from the color panels, the same problem will be raised.

[0007] However, the complete classification of the glass members per group as described above requires much time and labor, and thus leads to the increase in production cost. Further, there is also a problem that a demand for the black-and-white CRT bulb glass is small and thus the production amount thereof is limited, so that complete recycling can not be achieved with respect to the black-and-white CRT bulb glass.

[0008] In view of the above, the color panels with the adhering frits and the black-and-white panels are now being recycled as a material of the funnel glass which is required to be PbO glass as described above.

[0009] The black-and-white panels, the color panels and the frits respectively contain colorants, such as NiO, Co₃O₄, MnO₂ and Cr₂O₃. Thus, if such recycling is performed, these colorants are mixed into the funnel glass. Even if CRTs are produced using the funnel glass with those colorants mixed therein, no particular problems will arise in view of characteristics thereof.

[0010] However, since the amount of the black-and-white panels, the color panels and the frits to be recycled is not fixed, the rate of the recycled glass contained in a material of the funnel glass changes and, following this, the amount of the contained colorants also changes. As a result, the infrared ray transmittance of the funnel glass is not fixed, so that upon producing the funnel glass in a glass melting furnace, the temperature at the bottom of the furnace fluctuates and thus the flow of a molten glass material is not stabilized, resulting in a possibility that the numbers of seeds and devitrifying stones increase to lower the product yield.

SUMMARY OF THE INVENTION

[0011] It is therefore an object of the present invention to provide a method of producing CRT funnel glass suitable for recycling glass containing a colorant.

[0012] It is another object of the present invention to provide CRT funnel glass wherein the infrared ray transmittance is stable.

[0013] Other objects of the present invention will become clear as the description proceeds.

[0014] As a result of repeating various experiments, the present inventors have found out that even if a colorant contained in a frit, a color panel or a black-and-white panel enters into funnel glass, the infrared ray transmittance of the glass can be stabilized by adding a given amount of Fe₂O₃ depending on an amount of the colorant. The present invention has been proposed in view of this finding.

[0015] According to one aspect of the present invention, there is provided a method of producing CRT funnel glass comprising the step of adding Fe₂O₃ in a range of 0.05 to 1 mass % into a glass material of said CRT funnel glass so that a fluctuation of transmittance of light having a wavelength of 1,050 nm is 10% or less in a thickness of 10 mm of said CRT funnel glass.

[0016] According to another aspect of the present invention, there is provided CRT funnel glass containing Fe₂O₃ in a range of 0.05 to 1 mass %.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] For producing CRT funnel glass, CRT panel glass or CRT frit is used as a glass material thereof. By adding Fe₂O₃ in a range of 0.05 to 1 mass % into the glass material, a fluctuation of transmittance of light having a wavelength of 1,050 nm is adjusted to be 10% or less in a thickness of 10 mm of the CRT funnel glass. Specifically, by adding a given amount of Fe₂O₃ depending on an amount of a colorant contained in the glass material, the infrared ray transmittance of the CRT funnel glass is stabilized. As a result, there can be obtained the CRT funnel glass whose infrared ray transmittance is stable, while its composition contains one or more colorants selected from the group consisting of NiO, Co₃O₄, MnO₂ and Cr₂O₃. Naturally, the obtained CRT funnel glass contains Fe₂O₃ in a range of 0.05 to 1 mass %.

[0018] In the foregoing producing method of the CRT funnel glass, Fe₂O₃ functions to lower the infrared ray transmittance of the glass like the colorant (NiO, Co₃O₄, MnO₂, Cr₂O₃) entering from the frit, the color panel or the black-and-white panel. Thus, by adjusting an adding amount of Fe₂O₃ depending on the content of the colorant, the infrared ray transmittance of the glass can be stabilized. As a result, the fluctuation of the temperature at the bottom of the melting furnace is suppressed to stabilize the flow of the molten glass material, so that the CRT funnel glass with less seeds and devitrifying stones can be obtained.

[0019] As described above, by adjusting an adding amount of Fe₂O₃ depending on the content of the colorant, the infrared ray transmittance of the glass can be stabilized. If the adding amount of Fe₂O₃ is less than 0.05 mass %, the fluctuation of the infrared ray transmittance of the glass can not be stabilized within 10% or less when the colorant amount fluctuates largely. On the other hand, if the adding amount of Fe₂O₃ is greater than 1 mass %, the infrared ray transmittance of the glass becomes so low that the heat can not reach the bottom of the melting furnace, thereby increasing the seeds and devitrifying stones. Preferably, the adding amount of Fe₂O₃ falls within a range of 0.08 to 1 mass %, and more preferably, within a range of 0.1 to 0.9 mass %. For suppressing generation of the seeds and devitrifying stones by increasing the infrared ray transmittance of the glass to allow the heat to reach the bottom of the melting furnace, it is desirable that the transmittance of light with a wavelength of 1,050 nm in a thickness of 10 mm of the glass is set to 50% or greater, preferably 60% or greater, and more preferably 70% or greater.

[0020] Further, the foregoing composition of the CRT funnel glass contains PbO in a range of 10 to 30 mass %. This realizes the X-ray absorption coefficient of 40 cm-1 or greater at 0.6 Å to provide the glass with a high X-ray shieldability, and further achieves a viscosity of the glass suitable for the formation.

[0021] Preferably, the composition of the glass contains, in mass %, 48 to 58% SiO₂, 0.5 to 6% Al₂O₃, 10 to 30% PbO, 0 to 5% MgO, 0 to 6% CaO, 0 to 9% SrO, 0 to 9% BaO, 3 to 9% Na₂O, 4 to 11% K₂O, 0 to 3% ZrO₂, 0 to 5% ZnO, and 0.05 to 1% Fe₂O₃. The reason for this glass composition will be explained hereinbelow.

[0022] SiO₂ is a component serving as a network former of the glass. If the content of SiO₂ falls within a range of 48 to 58 mass %, the formation becomes easy, and further, the matching with the thermal expansion coefficient of neck glass is improved. Preferably, the content of SiO₂ falls within a range of 50 to 57 mass %.

[0023] Al₂O₃ is also a component serving as a network former of the glass. If the content of Al₂O₃ falls within a range of 0.5 to 6 mass %, the formation becomes easy, and further, the matching with the thermal expansion coefficient of the neck glass is improved. Preferably, the content of Al₂O₃ falls within a range of 1 to 5 mass %.

[0024] PbO is a component which improves the X-ray absorption coefficient of the glass. If the content of PbO falls within a range of 10 to 30 mass %, the X-ray absorbability is sufficient, and further, the viscosity of the glass is suitable for the formation. Preferably, the content of PbO falls within a range of 15 to 27 mass %.

[0025] MgO is a component serving to facilitate melting of the glass and to adjust the thermal expansion coefficient and the viscosity. If the content of MgO is 5 mass % or less, the glass is reluctant to be devitrified and the liquidus temperature is low, so that the formation becomes easy. Preferably, the content of MgO is 4 mass % or less.

[0026] CaO, like MgO, is a component serving to facilitate melting of the glass and to adjust the thermal expansion coefficient and the viscosity. If the content of CaO is 5 mass % or less, the glass is reluctant to be devitrified and the liquidus temperature is low, so that the formation becomes easy. Preferably, the content of CaO falls within a range of 1 to 5 mass %.

[0027] Each of SrO and BaO is a component serving to facilitate melting of the glass, to adjust the thermal expansion coefficient and the viscosity, and to improve the X-ray absorbability. If the content of each of SrO and BaO is 9 mass % or less, the glass is reluctant to be devitrified and the liquidus temperature is low, so that the formation becomes easy. Preferably, the content of each of SrO and BaO is 7 mass % or less.

[0028] Na₂O is a component serving to adjust the thermal expansion coefficient and the viscosity. If the content of Na₂O falls within a range of 3 to 9 mass %, the matching with the thermal expansion coefficient of the neck glass is improved, and further, the viscosity of the glass is suitable for the formation. Preferably, the content of Na₂O falls within a range of 4 to 8 mass %.

[0029] K₂O, like Na₂O, is a component serving to adjust the thermal expansion coefficient and the viscosity. If the content of K₂O falls within a range of 4 to 11 mass %, the matching with the thermal expansion coefficient of the neck glass is improved, and further, the viscosity of the glass is suitable for the formation. Preferably, the content of K₂O falls within a range of 5 to 10 mass %.

[0030] ZrO₂ is a component which improves the X-ray absorption coefficient of the glass. If the content of ZrO₂ is 3 mass % or less, the glass is reluctant to be devitrified and the viscosity of the glass is not increased, so that the formation becomes easy. Preferably, the content of ZrO₂ is 2 mass % or less.

[0031] ZnO, when the content thereof is 5 mass % or less, improves the X-ray absorption coefficient of the glass and suppresses alkali elution. Preferably, the content of ZnO is 4 mass % or less.

[0032] If the frits, the glass members of the color panels or the glass members of the black-and-white panels are recycled for a material of the funnel glass, it is not possible to avoid entering of at least one kind from among the colorants of NiO, Co₃O₄, MnO₂ and Cr₂O₃. If an entering amount of these colorants is too much, the infrared ray transmittance of the glass becomes too low. Thus, the heat can not reach the bottom of the melting furnace, leading to a possibility of increment of the seeds and devitrifying stones. In view of this, it is desirable that the total amount of the colorants is 10,000 ppm or less.

[0033] Hereinbelow, CRT funnel glass will be explained using examples according to the preferred embodiment of the present invention and comparative examples.

[0034] Table 1 shows a composition of panel glass and a composition of funnel glass. TABLE 1 PANEL FUNNEL composition (mass %) SiO₂ 61.45 51.00 Al₂O₃ 2.00 4.00 PbO — 23.50 MgO — 2.50 CaO — 4.00 SrO 9.00 — BaO 9.00 — Na₂O 7.50 7.50 K₂O 7.50 8.00 ZrO₂ 1.50 — ZnO 0.50 — TiO₂ 0.50 — Sb₂O₃ 0.50 0.50 CeO₂ 0.50 — Fe₂O₃ 0.05 0.03 NiO 30 ppm — Co₃O₄ 300 ppm —

[0035] Table 2 shows examples (samples Nos. 1 to 5) according to the preferred embodiment of the present invention, and Table 3 shows comparative examples (samples Nos. 6 to 10). TABLE 2 EXAMPLES No.1 No.2 No.3 No.4 No.5 composition (mass %) SiO₂ 51.0 51.4 52.9 53.7 55.8 Al₂O₃ 3.9 3.8 3.6 3.4 3.0 PbO 22.3 21.2 18.8 16.5 11.8 MgO 2.4 2.3 2.0 1.8 1.3 CaO 3.8 3.6 3.2 2.8 2.0 SrO 0.5 0.9 1.8 2.7 4.5 BaO 0.5 0.9 1.8 2.7 4.5 Na₂O 6.6 6.6 6.7 6.8 7.0 K₂O 8.0 8.0 7.9 7.9 7.8 ZrO₂ 0.1 0.2 0.3 0.5 0.8 ZnO — 0.1 0.1 0.2 0.3 TiO₂ — 0.1 0.1 0.2 0.3 Sb₂O₃ 0.5 0.5 0.5 0.5 0.5 CeO₂ — 0.1 0.1 0.2 0.3 Fe₂O₃ 0.4 0.3 0.2 0.1 0.1 NiO 15 ppm 30 ppm 60 ppm 90 ppm 150 ppm Co₃O₄  2 ppm  3 ppm  6 ppm  9 ppm  15 ppm panel using rate (%) 5 10 20 30 50 crucible bottom 1400 1400 1400 1400 1400 temperature (° C.) X-ray absorption 65 64 60 57 50 coefficient (0.6 Å, cm⁻¹) infrared ray 64 64 64 64 64 transmittance (%)

[0036] TABLE 3 COMPARATIVE EXAMPLES No. 6 No. 7 No. 8 No. 9 No. 10 composition (mass %) SiO₂ 51.37 51.67 53.07 53.76 55.86 Al₂O₃ 3.9 3.8 3.6 3.4 3.0 PbO 22.3 21.2 18.8 16.5 11.8 MgO 2.4 2.3 2.0 1.8 1.3 CaO 3.8 3.6 3.2 2.8 2.0 SrO 0.5 0.9 1.8 2.7 4.5 BaO 0.5 0.9 1.8 2.7 4.5 Na₂O 6.6 6.6 6.7 6.8 7.0 K₂O 8.0 8.0 7.9 7.9 7.8 ZrO₂ 0.1 0.2 0.3 0.5 0.8 ZnO — 0.1 0.1 0.2 0.3 TiO₂ — 0.1 0.1 0.2 0.3 Sb₂O₃ 0.5 0.5 0.5 0.5 0.5 CeO₂ — 0.1 0.1 0.2 0.3 Fe₂O₃ 0.03 0.03 0.03 0.04 0.04 NiO 15 ppm 30 ppm 60 ppm 90 ppm 150 ppm Co₃O₄  2 ppm  3 ppm  6 ppm  9 ppm  15 ppm panel using 5 10 20 30 50 rate (%) crucible bottom 1480 1460 1440 1420 1410 temperature (° C.) X-ray absorption 65 64 60 57 50 coefficient (0.6 Å, cm⁻¹) infrared ray 84 81 77 74 69 transmittance (%)

[0037] Each of the samples given in Tables 2 and 3 was prepared in the following manner.

[0038] First, the panel glass having the composition defined in Table 1 was comminuted and mixed with a material batch at the using rate shown in Table 2 or 3 to prepare a funnel glass mixed batch. Then, the mixed batch was put into a clay crucible having a thermocouple arranged at the bottom thereof. Subsequently, the mixed batch was melted at 1,550° C. for 6 hours in a melting furnace wherein the crucible was heated only from its upper side, and then the temperature at the bottom of the crucible was measured.

[0039] In the compositions shown in Tables 2 and 3, SrO, BaO, ZrO₂, ZnO, NiO and Co₃O₄ were entered from the panel glass.

[0040] Then, for each of the samples thus obtained, the X-ray absorption coefficient and the infrared ray transmittance were derived. The results are shown in Tables 2 and 3.

[0041] The X-ray absorption coefficient was obtained by calculating the absorption coefficient at a wavelength of 0.6 Å with reference to the glass composition and the density.

[0042] The infrared ray transmittance was obtained by measuring the transmittance of light with a wavelength of 1,050 nm using an infrared spectrophotometer after each sample was subjected to optical polishing to have a thickness of 10 mm.

[0043] As seen from Table 2, with respect to the samples Nos. 1 to 5 of the examples according to the preferred embodiment, even when the total amount of the colorants changed, the infrared ray transmittance was kept constant by adjusting the amount of Fe₂O₃, so that the temperature of the bottom of the crucible was held constant. Further, the X-ray absorption coefficients were high, i.e. 50 cm⁻¹ or greater.

[0044] In contrast, with respect to the samples Nos. 6 to 10 of the comparative examples shown in Table 3, adjustment of the infrared ray transmittance using Fe₂O₃ was not carried out. Thus, as seen from Table 3, as the total amount of the colorants increases, the infrared ray transmittance was lowered and hence the temperature at the bottom of the crucible was lowered.

[0045] Then, the glass qualities were compared between glass obtained by putting the mixed batches of the samples Nos. 1 to 5 in order into a continuous melting furnace and melting them, and glass obtained by putting the mixed batches of the samples Nos. 6 to 10 in order into the continuous melting furnace and melting them.

[0046] As a result, in the former case using the mixed batches of the samples Nos. 1 to 5, there was no fluctuation of the infrared ray transmittance and thus no fluctuation of the temperature at the bottom of the melting furnace, so that generation of seeds and devitrifying stones in the glass were suppressed and the stable glass quality was obtained.

[0047] On the other hand, in the latter case using the mixed batches of the samples Nos. 6 to 10, the infrared ray transmittance fluctuated by 15% to cause large fluctuation of the temperature at the bottom of the melting furnace, so that a large number of seeds and devitrifying stones were generated.

[0048] In the foregoing preferred embodiment, the panel glass with no adhering frit is used. However, the same method can also be used even when the panel glass with adhering frit containing MnO₂ and Cr₂O₃ is used. Further, when using the frit or the panel glass as a funnel glass material, PbO, Al₂O₃ or the like may be added to adjust the X-ray absorption coefficient and the viscosity to obtain desired characteristics. 

What is claimed is:
 1. A method of producing CRT funnel glass, comprising the step of adding Fe₂O₃ in a range of 0.05 to 1 mass % into a glass material of said CRT funnel glass so that a fluctuation of transmittance of light having a wavelength of 1,050 nm is 10% or less in a thickness of 10 mm of said CRT funnel glass.
 2. The method according to claim 1, wherein CRT panel glass is used as said glass material.
 3. The method according to claim 1, wherein CRT frit is used as said glass material.
 4. The method according to claim 1, wherein said CRT funnel glass has a glass composition containing a colorant comprising at least one selected from the group consisting of NiO, Co₃O₄, MnO₂ and Cr₂O₃.
 5. CRT funnel glass containing Fe₂O₃ in a range of 0.05 to 1 mass %.
 6. The CRT funnel glass according to claim 5, which is produced from a glass material including CRT panel glass.
 7. The CRT funnel glass according to claim 5, which is produced from a glass material including CRT frit.
 8. The CRT funnel glass according to claim 5, wherein said CRT funnel glass has a glass composition containing a colorant comprising at least one selected from the group consisting of NiO, Co₃O₄, MnO₂ and Cr₂O₃.
 9. The CRT funnel glass according to claim 8, wherein transmittance of light with a wavelength of 1,050 nm in a thickness of 10 mm of said CRT funnel glass is 50% or greater.
 10. The CRT funnel glass according to claim 8, wherein the content of said colorant is 10,000 ppm or less.
 11. The CRT funnel glass according to claim 5, wherein said CRT funnel glass has a glass composition containing, in mass %, 48 to 58% SiO₂, 0.5 to 6 % Al₂O₃, 10 to 30% PbO, 0 to 5% MgO, 0 to 6% CaO, 0 to 9% SrO, 0 to 9% BaO, 3 to 9% Na₂O, 4 to 11% K₂O, 0 to 3% ZrO₂, 0 to 5% ZnO, and 0.05 to 1% Fe₂O₃. 